Heretofore, there have been known throttle valve drive mechanisms provided in outboard engine units, in which a valve shaft of a throttle valve is driven via a throttle cable. One example of such throttle valve drive mechanisms is disclosed in Japanese Patent Application Laid-Open Publication No. HEI-07-286559 (JP H07-286559 A). FIG. 10 hereof illustrates a basic construction of the throttle valve drive mechanism disclosed in JP H07-286559 A. Operating link mechanism 200 for an engine provided on an outboard engine unit includes: a pulley 202 having throttle cables 201a and 201b wound thereon; a cam 203 provided on the outer periphery of the pulley 202; an accelerator 205 operable by being pushed by the cam 203; an accelerator rod 206 provided on the accelerator 205; and a throttle valve pivot shaft 207 connected to the rod 206. In the disclosed throttle valve drive mechanism, a pivot shaft 211 of the accelerator 205 for driving the rod 26, a pivot shaft 212 of the cam 203 and the throttle valve pivot shaft 207 are disposed in parallel to one another.
However, because the above-mentioned three shafts 211, 212 and 207 are disposed in parallel to one another and because the rod 206, throttle cables 201a and 201b, etc. are provided around the shafts 211, 212 and 207, the throttle valve drive mechanism may undesirably increase in size in a direction perpendicular to the shafts 211, 212 and 207. Thus, although there is a great demand for reducing a size of a section around the throttle valve as in most outboard engine units having great spatial limitations, the throttle valve drive mechanism disclosed in JP H07-286559 A would prevent reduction in size of the section around the throttle valve.